| There are significant morphological differences between embryos of different species before implantation.The embryos of humans and mice do not undergo significant morphological changes before implantation,while pig embryos undergo significant changes in shape from spherical to oval,then tubular,and finally filamentous before implantation.Studies have shown that this drastic morphological change in pig embryos is necessary for successful implantation,and the process involves cell proliferation,cell rearrangement,and inflammatory reactions.Changes in cell state are often accompanied by adjustments in metabolic patterns.However,the metabolic dynamics of cells during the elongation process of pig embryos are still unclear,and the composition of uterine flush and metabolic changes in the endometrium during this process also need to be studied.Firstly,this study investigated the development of pig embryos on day 8,10,and 12 from a transcriptomic perspective,and found that the metabolic mode of the TE cells changed from oxidative phosphorylation to glycolysis during the elongation period of embryo development on day 10.Further analysis of genes related to the tricarboxylic acid cycle,amino acid,lipid,and nucleotide metabolism revealed that the proportion of lipid metabolism-related gene expression increased significantly on day 10,including long-chain fatty acid transport and metabolism-related genes expressed on day 10 and 12,especially the fatty acid transport protein SLC27A4 highly expressed in the trophoblast on day 10,while the limiting enzyme ofβ-oxidation,CPT1 A,was highly expressed in the trophoblast on day 12.To validate these results,immunofluorescence detection was performed on SLC27A4 and CPT1 A in the trophoblast,which also showed high expression specificity for each stage.These results suggest that lipid metabolism may be the main energy source during the proliferation and morphological changes of the trophoblast.Subsequently,targeted detection of metabolites in uterine flush on day 8,10,and 12 was conducted.The data showed that the content of saccharides metabolites suddenly increased on day 10 and then decreased on day 12,while amino acid metabolites were relatively stable,gradually increasing from day 8 to day 10 and then decreasing on day 12.Nucleotide and derivative metabolites were highest on day 8 and gradually decreased by day 12,while lipid metabolites were highest on day 8,decreased on day 10,and then increased again on day 12.Finally,to determine the source of fatty acids in the uterine flush,immunohistochemical experiments were performed to detect the expression of SLC27A4 protein in the endometrium.The results showed that SLC27A4 was expressed in the endometrium on day 8,10,and 12 of embryonic development,indicating that the endometrium participates in the transport of fatty acids during embryonic elongation.Based on the above research results,the following conclusions can be drawn: 1)the sugar metabolism of the nourishing layer during the elongation period of pig embryos changes from oxidative phosphorylation to aerobic glycolysis;2)the content of sugar metabolites in the uterine environment during the elongation period of pig embryos is stage-specific;3)fatty acid oxidation may be the main source of energy for cell proliferation and migration during the elongation of the TE,and the fatty acids in the uterine flush may come from the transport of the endometrium.In conclusion,this study provides a new perspective on the metabolic pattern of the TE during the elongation stage of pig embryos,and also provided a reference for the establishment of porcine in vitro embryo culture system from the perspective of metabolism. |
